Article pubs.acs.org/jpr
Plasma 25-Hydroxyvitamin D, Hormonal Contraceptive Use, and the Plasma Proteome in Caucasian, East Asian, and South Asian Young Adults Bibiana García-Bailo,†,‡ Joseph Jamnik,† Laura A. Da Costa,† Christoph H. Borchers,§ Alaa Badawi,‡ and Ahmed El-Sohemy*,† †
Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, ON, Canada Office of Biotechnology, Genomics, and Population Health, Public Health Agency of Canada, Toronto, ON, Canada § University of Victoria-Genome British Columbia Proteomics Centre, University of Victoria, Victoria, BC, Canada ‡
S Supporting Information *
ABSTRACT: Vitamin D affects gene expression, but its downstream effects on the proteome are unclear. Hormonal contraceptives (HC), which affect vitamin D metabolism and have widespread effects on the plasma proteome, may confound the association between vitamin D and the proteome. We determined whether HC use modified the association between 25-hydroxyvitamin D (25D) and a panel of 54 high-abundance plasma proteins. Cross-sectional analyses were conducted in healthy, nonsmoking female HC users (n = 216), female HC nonusers (n = 502), and men (n = 301) from Toronto, Canada. Plasma 25D was measured by HPLC−MS/MS, and proteins were measured by LC-multiple-reaction-monitoring (MRM)-MS. The 54 proteins clustered into four distinct proteomic profiles. A positive association was observed between Profile 1, containing positive acute phase proteins, and 25D. In female HC users, a Jshaped association existed between Profile 1 and 25D, but no associations existed in female HC nonusers and men. Twelve proteins were individually associated with 25D in female HC users, but only two were associated with 25D in female HC nonusers and no associations were observed in men. After accounting for hormone dose, only three proteins were associated with 25D. In summary, HC use is an important confounder of the association between circulating 25D and numerous plasma proteins. KEYWORDS: vitamin D, proteomics, plasma proteins, hormonal contraceptives, acute phase proteins, young adults
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INTRODUCTION
abundant circulating form of vitamin D, and it is the accepted functional biomarker of vitamin D status.2 Conversion of 25D to 1-α-dihydroxyvitamin D (1,25D), the main biologically active form of the vitamin, occurs through hydroxylation in the kidney and other target tissues.11 The latter form of vitamin D is a steroid hormone that affects both the regulation of target gene transcription and the activation of various signal transduction pathways when it binds to the vitamin D receptor (VDR), a transcription factor with effects on numerous tissues.11 Recent in vitro studies have examined vitamin D action across the genome, using gene expression and chromatin immunoprecipitation techniques.12,13 Hundreds of target genes, belonging mainly to immune and signaling pathways, have been identified, and many are known to be associated with diseases such as type 1 diabetes, Crohn’s disease, multiple sclerosis, and colorectal cancer.12 However, it is not known
Cardiometabolic disease, including type 2 diabetes and cardiovascular disease, represents a global health problem.1 Vitamin D has been examined extensively as a potentially preventive factor in the development of cardiometabolic and other chronic diseases.2 However, as summarized by recent systematic reviews, the evidence from epidemiologic studies and clinical trials is inconclusive.3−5 The inconsistencies between studies may result not only from differences in methodology, but also from a lack of adequate biomarkers, unaccounted confounders from various demographic and lifestyle factors, and genetic differences both within and between populations.6 The protective actions of vitamin D on cardiometabolic disease are thought to occur through modulation of physiologic processes that become dysregulated during disease progression, such as inflammation and pancreatic β-cell function.7−10 Vitamin D, obtained through cutaneous sunlight exposure or through the diet, is hydroxylated in the liver to 25hydroxyvitamin D (25D).11 This metabolite is the most © 2013 American Chemical Society
Received: December 6, 2012 Published: February 22, 2013 1797
dx.doi.org/10.1021/pr4001042 | J. Proteome Res. 2013, 12, 1797−1807
Journal of Proteome Research
Article
excluded from the analyses reported here because of insufficient sample size to make adequately powered comparisons. On the basis of the date of blood draw, individuals were classified by seasons: spring (March, April, May), summer (June, July, August), fall (September, October, November), and winter (December, January, February).
whether the observed widespread effects of vitamin D at the genome level in vitro translate into downstream effects at the level of the proteome in vivo. Over 3000 proteins have been identified in the human plasma proteome.14,15 Among the most abundant, ranging in concentration between
